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From:   KP Singh <kpsingh@chromium.org>
Date:   Tue, 3 Mar 2020 23:25:45 +0100
To:     Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc:     open list <linux-kernel@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Paul Turner <pjt@google.com>,
        Florent Revest <revest@chromium.org>,
        Brendan Jackman <jackmanb@chromium.org>
Subject: Re: [PATCH bpf-next 0/7] Introduce BPF_MODIFY_RET tracing progs.
Message-ID: <20200303222545.GB3272@chromium.org>
References: <20200303140950.6355-1-kpsingh@chromium.org>
 <CAEf4BzZkkbf0a-pCcmxq6+=XdJH6H7pPwbzq=UiMKRpWnJceyA@mail.gmail.com>
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On 03-M?r 14:12, Andrii Nakryiko wrote:
> On Tue, Mar 3, 2020 at 6:12 AM KP Singh <kpsingh@chromium.org> wrote:
> >
> > From: KP Singh <kpsingh@google.com>
> >
> > This was brought up in the KRSI v4 discussion and found to be useful
> > both for security and tracing programs.
> >
> >   https://lore.kernel.org/bpf/20200225193108.GB22391@chromium.org/
> >
> > The modify_return programs are allowed for security hooks (with an
> > extra CAP_MAC_ADMIN check) and functions whitelisted for error
> > injection (ALLOW_ERROR_INJECTION).
> >
> > The "security_" check is expected to be cleaned up with the KRSI patch
> > series.
> >
> > Here is an example of how a fmod_ret program behaves:
> >
> > int func_to_be_attached(int a, int b)
> > {  <--- do_fentry
> >
> > do_fmod_ret:
> >    <update ret by calling fmod_ret>
> >    if (ret != 0)
> >         goto do_fexit;
> >
> > original_function:
> >
> >     <side_effects_happen_here>
> >
> > }  <--- do_fexit
> >
> > ALLOW_ERROR_INJECTION(func_to_be_attached, ERRNO)
> >
> > The fmod_ret program attached to this function can be defined as:
> >
> > SEC("fmod_ret/func_to_be_attached")
> > BPF_PROG(func_name, int a, int b, int ret)
> 
> nit: int BPF_PROG(...)

Noted. Thanks!

- KP

> 
> 
> > {
> >         // This will skip the original function logic.
> >         return -1;
> > }
> >
> > KP Singh (7):
> >   bpf: Refactor trampoline update code
> >   bpf: JIT helpers for fmod_ret progs
> >   bpf: Introduce BPF_MODIFY_RETURN
> >   bpf: Attachment verification for BPF_MODIFY_RETURN
> >   tools/libbpf: Add support for BPF_MODIFY_RETURN
> >   bpf: Add test ops for BPF_PROG_TYPE_TRACING
> >   bpf: Add selftests for BPF_MODIFY_RETURN
> >
> >  arch/x86/net/bpf_jit_comp.c                   | 261 +++++++++++++-----
> >  include/linux/bpf.h                           |  24 +-
> >  include/uapi/linux/bpf.h                      |   1 +
> >  kernel/bpf/bpf_struct_ops.c                   |  13 +-
> >  kernel/bpf/btf.c                              |  27 +-
> >  kernel/bpf/syscall.c                          |   1 +
> >  kernel/bpf/trampoline.c                       |  66 +++--
> >  kernel/bpf/verifier.c                         |  32 +++
> >  kernel/trace/bpf_trace.c                      |   1 +
> >  net/bpf/test_run.c                            |  57 +++-
> >  tools/include/uapi/linux/bpf.h                |   1 +
> >  tools/lib/bpf/libbpf.c                        |   4 +
> >  .../selftests/bpf/prog_tests/fentry_fexit.c   |  12 +-
> >  .../selftests/bpf/prog_tests/fentry_test.c    |  14 +-
> >  .../selftests/bpf/prog_tests/fexit_test.c     |  69 ++---
> >  .../selftests/bpf/prog_tests/modify_return.c  |  65 +++++
> >  .../selftests/bpf/progs/modify_return.c       |  49 ++++
> >  17 files changed, 509 insertions(+), 188 deletions(-)
> >  create mode 100644 tools/testing/selftests/bpf/prog_tests/modify_return.c
> >  create mode 100644 tools/testing/selftests/bpf/progs/modify_return.c
> >
> > --
> > 2.20.1
> >